One requirement which arises in a number of different contexts is that of covering an elongate opening using a cover which can be readily removed to allow access into the opening. One particular situation where this may occur and for which the present invention is primarily but not exclusively designed is that of a composting pit. Such a pit is generally wider than 10 feet allowing ready access to the pit for entry into the pit of vehicles and can be as much as 20 feet in width and is of a long length many times greater than the width.
Composting of materials is an effective and environmentally desirable technique for disposing of waste materials since the natural composting process breaks down any undesirable materials generally leaving a usable compost material.
However one significant problem which arises with composting methods of this type is that the composting action gives off noxious gases or at least foul smelling gases which are unacceptable to any surrounding persons in a residential or even a work environment.
It is being proposed therefore for such elongate pits to be covered by a series of doors which extend over the pit but can be opened and closed to allow access to the materials within the pits. It will be appreciated that the composting process requires that the material be mixed or agitated and that additional elements in some cases should be added including water and any necessary accelerators. The operation on the material within the pit is carried out by a machine or vehicle which runs along the pit on rails one on each side of the pit so that the machine bridges the pit and can operate below the rails within the material in the pit. The individual doors are then opened as the machine is moved forward and closed behind the machine thus maintaining the majority of the pit closed as the machine moves along the pit. However these doors are unsatisfactory in that they are difficult to seal and require extensive manual operation for the opening and closing action.